Generally several kinds of rubber components are blended to a crosslinked rubber composition used for a tire tread depending on required performances. It is known that when rubber components of different kinds are present, since compatibilities of each rubber component with a filler are different from each other, a filler is unevenly distributed, namely, filler distribution is inferior.
It is considered that uneven distribution of a filler leads to lowering of dispersibility of a filler, which deteriorates breaking resistance and abrasion resistance. This is because if dispersibility of a filler is not good, the filler is agglomerated and the agglomerated filler becomes a starting point of breakage, thereby leading to deterioration of breaking resistance and abrasion resistance.
Thus various technologies for enhancing dispersibility of a filler in a crosslinked rubber composition have been proposed (Patent Document 1, etc.). However, good dispersibility does not necessarily lead to excellent breaking resistance and abrasion resistance, and there is an exception. Namely, sometimes there is a phenomenon such that though dispersibility of a filler in a crosslinked rubber composition is good, good results cannot be obtained from measurement of abrasion resistance of this crosslinked rubber composition and a rubber product thereof.
In order to make a mechanism of causing such an exception clear, breakage and friction phenomena have been observed by means of various methods. However, the mechanism has not been made clear completely.
Meanwhile, an X-ray computerized tomography is known as a technology for analyzing a material constituting a solid sample and a low density region contained in an inside thereof. For example, Patent Document 2 describes a method of visually analyzing a material constituting a friction member and a low density region contained inside thereof. However, analyzing a sample material in a state, such as elongated, of being applied with an external energy or analyzing a density of the material is not described in Patent Document 2.